As a counterexample, Yesod (A Rails-like web framework for Haskell) uses (very appropriate IMO) external DSLs for defining URL routing and the data model. These are not runtime config, they are parsed into Haskell code, typechecked and compiled ahead of time:

models: https://github.com/snoyberg/haskellers/blob/master/config/mo...

routes: https://github.com/snoyberg/haskellers/blob/master/config/ro...